Very good things have been said, particularly by Ramsus and Lord J, and I generally agree with them all.
Those should be the rules. However, with all rules, they can be broken at times. Particularly, those governing the complexity of words.
Now, generally, I'll agree with you. That, in fact, is one of my own issues with writing - using overly long, technical, complex, or worst of all, inordinately antiquated words, particularly in fantasy writing. To speak for myself, I used to use, say, oft for often, aught for anything, but in time found these all to be rather too assuming and false-sounding, and ammended nearly all of them to their modern equivalent. The same goes for most anything using the older pronouns. Whence, wither, and the like, are marginal. Also annoying are the complex ones, but I'll get to that later.
However, there are some times when the rules can be broken. When I write, I sometimes draw things out, for example, and very, very often use two words where one would do, if I happen to like the sound of the two. Now, this is for the cause of feeling. Not everyone will like it, I'm certain (for example, making use of the Epic Simile will not make people favour my writing, I'm certain. Not that I use it much, but at times my simile will go on for several sentences.) Now, the vindication is this: I'm doing that in the service of style. I'm trying to bring across a certain mood (in this case, semi-epic), and the word choice, and syntax, must reflect that. For epic, it must be ponderous, and so on. The same word choice will obviously not work everywhere. Here's an example from a fantasy story I read, a choice of words that really caught my eye as wrong. In speaking of a sunrise, the author used 'conflagration'. Now, maybe it is just me, but that's a bloated word for a sunrise in a fantasy story. For a contemporary story, it's admissable, but something meant to be in a middle-ages setting? Why not merely use 'fire', or modify 'fire' with some other adjective, rather than use such a fancy word? Now, I will myself use fancy words (many of which I later return to remove in favor of more common ones, seeing it as a foolish decision), ie. sigaldry (that's just my favorite, so it's staying in despite of its obsolete nature), array... whatever. The main point is, however, that one keeps true to the feel. I like to experiment with words, with syntax... whatever.
But in the end, what's important is that it keeps true to the feel, and that it doesn't sound as if you've just used a thesaurus to find a fancy synonymn. I think that's the middle ground there - and likely what both Ramsus and Lord J were speaking of. Use big words, yes... but ONLY if you know what you're doing, if you're doing it for a reason, and have control of it. If it serves no more purpose than attempting to make oneself appear clever, it's a bad thing.
